Fractionation of coal tar materials



y 29, 1934- G. L. PARKHURST 1,960,679

FRACTIONATION OF COAL TAR MATERIALS Filed Oct. 3, 1932 Jaye Cfiamber a INVENTOR Patented May 29,1934 I UNITED STATES 1,960,019 FRAOTIONATION or com. ran m'mamns George L. Parkhurst, Chicago, 111., assignor' to Standard Oil Company, Chicago, Ill., acorporation of Indiana Application October 3, 1932, Serial No. 635,929

18 Claims. (01.196-76) My invention relates to the solvent fractionation and purification of coal tar, coal tar fractions and partially refined coal tar products by means of liquefied normally gaseous hydrocarbons. Itis to be understood that in many cases my invention in certain of its various forms can also be applied to other direct or indirect products of the destructive distillation of coal-like materials, for instance, tar from the low temperature carbonization of coal, producer gas tar, blast furnace tar, water gas tar, oil gas tar, distillates and fractions of these various tars and partially refined products thereof. All of these various materials will be referred to collectively as coal tar materials.

An object of my invention is to provide a process for the fractionation of coal .tar materials into two or more materials differing from each other ancl from the original coal tar material in chemical and physical properties. Another object is to provide a, process for the purification of coal tar materials in order to render them more suitable for various types of uses. A further object is to provide a process capable of accomplishing the aforementioned objects efficiently, inexpensively and with substantially no loss or destruction of any of the constituents of the coal tar material to which the process is applied. Still further objects of my invention will become apparent as the description thereof proceeds.

Although it will be apparent that my process, and the apparatus suitable for practicing it, is subject to many modifications as applied to various types of coal tar materials for various purposes, I will first describe the process and appa ratus in general terms by reference to the accompanying drawing which is a conventionalized flow diagram and then proceed to a description of some representative specific applications.

Referring now more particularly to the draw,- ing, receptacle 1 isa. stor ge receptacle for the solvent used in my process hich may suitably be a liquefied normally gaseous hydrocarbon such as ethane, propane, butane, isobutane, propylene, butylene or a mixture of two or more of these. It will be understood that other liquefied normally gaseous substances may sometimes suitably be used. Receptacle 1 is placed under pressure and/or provided with refrigeration and insulation mixer 6, which may be of any type, continuous or batch, for instance, a multiple orifice mixer,

be treated which is simultaneously introduced into mixer 6 by means of pump '1 from suitable storage notshown.

It is generally, but by no means always, desirable to lower the temperature of the material coming out of mixer 6 in order to promote its separation into the desired fractions. This cooling can, at least in part, be obtained efficien ly by passing the material from mixer 6 through valve 8 and heat exchanger 9, shown as a tubular heat exchanger cooled by one of the intermediate products of the process. However, by closing. valves 8 and 10 and opening valve 11, heat exchanger 9 may be by-passed if it is not desired to use this indirect cooling. Ineither vcase the stream passes through valve 12 and/or valve 13 for further treatment as desired.

It is to be understood that the temperature of the materials undergoing mixing and the ratio expansion valve 15, into chiller 16 where a temperature reduction is obtained by withdrawing a portion of the solvent in vapor form through valve 17. Baffles 18 are used to prevent the carrying over of liquid material with the vapors withdrawn throughvalve 17. The chilled material from the bottom of chiller 16 is withdrawntherefrom through valve 19 by means of pump 20 and passed through valve 21 and, if desired, expansion valve 22 into separator 23 where, in general, there is a separation into two layers, the heavier being withdrawn through valve 24 by means of pump 25 and the lighter being withdrawn through valve 26 by means of pump 27. Solvent vapors can be withdrawn from separator 23, if desired,

through valve 28, thereby accomplishing a further chilling. If this is done it is desirable to use baffles 29 similar to baiiles 18.

If a separate evaporative chilling step is not desired, chiller 16 is by-passed by closin valves 14, 15, 17, 19 and 30 and opening valves 31 and 32, thereby introducing the materialfrom mixer 6 or heat exchanger 9 directly into separator 23. The material withdrawn through valve 24 is introduced through expansion valve 33, if desired, into flash drum 34 where the solvent vapors are removed by the application of heat through steam coils and/or by reducing the pressure by adjustment of valves 33, 36 and 38. Battles 3'1 can suitably be used inthe upper part of flashdmm 34 to prevent entrainment. This fraction of the original coal tar material, stripped of solvent, is withdrawn from flash drum 34 through valve 38 and passed to a storage receptacle 39 from which it can be withdrawn as desired through valve 40 for further treatment or use.

The lighter material from separator 23, containing, in general, the bulk of the solvent is, as

aforementioned, withdrawn through valve 26 by means of pump 27. If it is desired to utilize its capacity to absorb low temperature heat this material is then passed through valve 41 and heat exchanger 9 '(valve 42 being closed) where it comes in indirect heat exchange relationship with the material entering the process. However, by closing valve 41 and opening valve 42, heat exchanger 9 can be by-passed. In either case the stream passes through valve 43 into flash drum 44, similar to flash drum 34, equipped with bailles 45 and steam coils 46. Solvent vapors are removed from flash drum 44 through valve 47 just as from flash drum 34 and the stripped product is withdrawn through valve 48 to storage receptacle 49 from which it can be withdrawn through valve 50 for further treatment or use as desired.

It will be readily understood that should it be so desired, the heavier material from separator 23, i. e., the material withdrawn through valve 24 may also be utilized to cool the material en- I tering the process. However, the material withdrawn through valve 24'will, in general, be more viscous and of lesser volume than that withdrawn through valve 26, and for this reason it is preferred to utilize the capacity of the lighter material to absorb low temperature heat and to pass a the heavier material from separator 23 directly to flash drum 34.

In order to make up for losses and/or to supply further solvent for refrigeration purposes, additional liquefled solvent from storage receptacle 1 can be introduced directly into chiller 16 and/or separator 23 by means of pump 4. To introduce additional solvent into chiller 16 valves 51 and 30 are opened and to introduce additional solvent into separator 23 valves 51, 52 and 53 are opened. The amount introduced can be controlled by regulation of these valves.

The hereinbefore described modes of procedure are particularly adapted to operation on acontinuous basis, liquefied solvent and raw coal tar material being continuously fed to the process and the products of the process being continuously withdrawn. However, in certain cases it will be found desirable to operate at least partially on a batch basis and this can be accomplished by passing the material from mixer 6 orheat exchanger 9 through valve 13 instead of (or in addition to) through valve 12 and into settler 51. Sometimes it will be preferred to further chill the incoming material by self-refrigeration and in this case the incom'n'g material can be passed through valves 12, 14 and 15 into chiller 16 and withdrawn therefrom by means of valve 19, pump 20 and valve 52 into settler 51.

Ineither case material will be introduced to settler 51 until the settler is filled to a convenient level. If further temperature reduction is desired, this can be accomplished by withdrawing vapors through valve 53 during and/orafter' I the admssion of material to settler 51.

The process according to this modification is sooperated that the material in settler 51 will as in the continuous modification of my process withdrawn, valve 57 is opened and the lower layer 'sary to introduce steam through coil 61' to inseparate into two layers over a period of time, and when this has been accomplished the upper layer is withdrawn by means of pump 55 through one of valves 54, preferably that one which appears to be located just above the meniscus between the two layers. This material is then passed through valve 56 and, if desired, reduction valve 43 into flash drum 44 where the solvent is removed in vapor form through valve 47 8 and the product is simultaneously withdrawn from flash drum 44 through valve 48 into storage receptacle 49 as, before. 7

When this upper layer from settler 51 has been is withdrawn by means of pump 58 and passed through valves 59 and 60 and, if desired, reduction valve 33 into flash drum 34 where solvent vapors are removed through valve 36 and the product is withdrawn through valve 38 into storage receptacle 39 asbefore.

When working on certain types of coal tar material, the lower layer from settler 51 will be highly viscous and in this event it may be, necescrease the temperature of the lower layer sufllciently to permit its withdrawal. Under some conditions it will be found advisable to introduce sufficient heat by means or steam coil 61 to com-- pletely drive off the solvent vapors through valve 53, and in this event, valve 59 is closed and valve 62 is opened, thereby passing the stripped lower layer directly into storage receptacle 63 from which it can be removed through valve 64 for further treatment or use as desired, for example, 1 as charging stock to a coking operation, asphalt manufacture or the like.

A still further alternative which can be applied to the material in settler 51 is to withdraw the lower layer first (without previously withdrawing the upper layer) through valve 57 by means of pump 58 passing it through valves 59 and 60 and, if desired, reduction valve 33 into flash drum 34 where residual solvent is removed in vaporv form. When the lower layer has thus been completely removed valve 57 is closed and valve 65 is opened, thereby passing the upper layer through valves 65, 56 and, if desired, valve 43 by means of pump 55 to flash drum 44 where residual solvent is removed in vapor form.

In any of these alternative modifications to be applied to the material in settler 51, the original coal tar material will be separated into two fractions which, after removal of solvent, will pass either into storage receptacles 39 and 49 130 or into storage receptacles 39 and 63.

In the foregoing description of my process, no mention has been made of the so-called overhead system, i. e., the portion of my process and apparatus adapted to the withdrawal of sol- 13-5- vent in vapor form from the various pieces of equipment; its compression, condensation and return to the process. It will be noted that solvent vapors can be withdrawn from any of the following pieces of equipment: chiller 16, separator 23, flash drum'34, flash drum 44 and/or settler 51. Vapors withdrawn from chiller 16 and/or separator 23 to pass to surge chamber 66 which is used to smooth out any unevenness which may occur in the withdrawal of vapors and provide a 1 reasonably constant supply of vapors for compressor 67 which is used to partially compress vapors from surge chamber 66 and pass them to surge chamber 68. Vapors withdrawn from flash drum 34, flash drum 44 and/or settler 51 will often be at a higher pressure than those withdrawn from chiller 16 and/or separator 23 due to the possibility of supplying heat to the firstmentioned pieces of equipment. In this case it is desirable to pass these vapors directly into surge chamber 68 by means of valve 69 without putting them through the relatively low pressure surge chamber 66. However, if it is so desired, or if additional heat is not supplied in flash drum 34, flash drum 44 and/or settler 51 these vapors may be passed into surge chamber 66 by opening valve 70 and closing valve 69. It will also be readily comprehended that in some instances it is desirable in the interest of simplicity to do away with one of these surge chambers entirely, or even to do away with both of them and directly compress the solvent vapors directly as withdrawn from any or all of the various items of equipment aforementioned.

Material from surge chamber 68 is further compressed by means of compressor 71 and passed through condenser 72 which may suitably be an ordinary coil condenser, water cooled, and thence through valve '73 into storage receptacle 1, thereby becoming available for re-use.

Having thus described my process and apparatus in general terms I will now proceed to a description of a few typical specific embodiments as applied to various types of coal tar materials.

It is well known that coal tar is a complex mixture of hundreds of chemical compounds, including hydrocarbons, oxygenated compounds, sulfur derivatives and nitrogenous compounds. Furthermore, it is well known that the types of compounds present in any particular tar and their relative proportions are dependent on the type of coal from which the tar is derived, the process in which the tar is produced, etc. Thus, for example, it is known that tars produced at relatively low temperatures, -for instance, by low temperature carbonization (1000 F. or even lower), are high in paraffinic hydrocarbons and other hydrocarbons having a high ratio of hydrogen to carbon as compared with tars produced at high temperatures (e. g., 1800 F.2000 F.). For this reason it will be understood that the exact procedure and working conditions to be used must be varied to suit the exigencies of any particular situation but this can readily be accomplished by simple experiment in the light of the principles herein discussed.

The liquefied normally gaseous hydrocarbons used in my process have a relatively high solvent power for the hydrocarbon constituents of a coal tar material as compared with their solvent power for the oxygen, sulfur and/or nitrogen-bearing constituents thereof. This fact is taken advantage of by treating the coal tar itself or a highboiling product of the fractional distillation thereof with my solvents at ordinary or slightly elevated temperature under pressure suflicient to keep the solvent in the liquid state. Under these conditions the great bulk of the hydrocarbons will be dissolved (with the exception of very heavy or tarry hydrocarbons) and the great bulk of the non-hydrocarbon constituents will remain undissolved. By this means it is possible to separate the original coal tar material by solvent fractionation with a liquefied normally gaseous hydrocarbon into two products, one of which will contain the bulk of the hydrocarbons and the other the bulk of the non-hydrocarbon constituents together with heavy tarry hydrocarbons. Each of these fractions can then be separated by fractional distillation or otherwise into constituents of various boiling points. Thus the soluble or hydrocarbon fraction can be separated into solvent naphtha, naphthalene, anthracene, etc.

Another, and very important, application of my process is to the purification of crude lght oils produced directly from the destructive distillation of coal and/or from the dist'llation of coal tar. These light oils contain as their principal constituents, hydrocarbons, phenols and pyridine bases. By treating such a light oil with a liqueved normally gaseous hydrocarbon, for instance, two to three times it volume of liquid propane; lowering the temperature, preferably by vaporizing a porton of the solvent, to a point at which the non-hydrocarbon constituents are insoluble (say 10 F. to 60 F.); separating the two liquid layers and removing the solvent it is possible to fractionate the light oil into a substantially hydrocarbon fraction and a phenolic and pyrdine fraction. This process has the advantage over those previously used that there is substantially no loss or destruction of material since the process is conducted at low temperature and is based on physical properties rather than on chemical reaction. Furthermore, the hydrocarbon fraction, being substantially free from the highly reactive phenolic and pyrid'ne impurities is more stable than that usually produced, i. e., it does not as readily form gums or darken on exposure to air and/or light. Similarly, the phenols produced are relatively pure and can be separated from the pyridine bases, if present, by means of a caustic wash more readily than if contam'nated with inactive hydrocarbon impurities.

Instead of applying my process to a crude light oil containing a variety of phenolic hydrocarbons and nitrogenous substances it is sometimes preferable to apply it to partially purified or segregated materials, such as crude carbolic acid, crude cresylic acid, crude benzol and/ or crude solvent naphthas which have been produced by fractional distillation and/or chemical treatment from the original coal tar material. Thus, for instance, crude phenol, crude tar acids or crude cresylic acid, normally contains substantal quantities of impurities soluble in my liquefied normally gaseous hydrocarbon solvents. By treating such a material with one of my solvents, preferably liquid propane, liquid ethane or a mixture of the two, and lowering the temperature to a point at which the phenolic substances are substantially completely insoluble (for instance 10 F. to F.), it is possible to separate two lquid layers, the upper containing the bulk of the solvent together with the hydrocarbon impurities and. the lower containing the phenolic constituents together with a small portion of the solvent. After separation of these layers the solvent can be removed by flashing and it will be found that a highly purified phenol, cresol or mixture of the two has been recovered and that a useful portion of benzol or solvent naphtha has been obta'ned as a by-product substantially uncontaminated with phenolic impurities. A similar process can be applied to the removal of impurities from crude pyridine.

Another coal tar material to which my process can suitably be applied is a hydrocarbon fraction such as crude benzol, crude toluol or crude solvent naptha. As normally produced, these substances tend to darken on exposure to light and/or air. They also tend to form gummy substances which decrease the value of the prodlubricants.

not and necessitate the use of expensive and dcstructive refining processes if it is desired to remove them. By treating such a material with my solvents it is possible to precipitate the im-.

purities at temperatures in the vicinity of -25 to F. without any chemical destruction of either the hydrocarbon material or the impurities, thereby producing a highly purified and stable benzol, toluol or naphtha and a valuable by-product. Y A somewhat similar process can be applied to the purification of crude naphthalene and crude anthracene. However, when working with these materials it must be remembered that they are much less soluble in the liquefied normally gaseous hydrocarbons than are the lighter hydroecarbon materials such as benzol, toluol andznaphtha. For this reason, when work ng with-them it is preferable to use a relatively high tempera+ ture (atmospheric or above) and a solvent of relatively high solvent power such as liquid butane. In this connection it maybe pointed out that the solvent powers of the liquefied nor* mally gaseous hydrocarbons increase with-increasing molecular Weight so that liquid propane is, in general, a better solvent than liquid ethane and liquid butane is, in general, a better solvent than liquid propane. After impurities have been separated from the naphthalene or anthracene solution by settling and/or filtration, the temperature can be reduced by permitting a portion of the solvent, e. g. butane, to evaporate, resulting in the crystallization of the naphthalene or anthracene in a relatively pure state. This may be settled out or filtered off and the filtrate processed as previously described.

Although in the ordinary high temperature coal tar the only paraffin hydrocarbons which are produced in quantities are the very high boiling waxy hydrocarbons and there is little or no material suitable for use as a lubricating-oil, this is not necessarily true of certain types of coal tar materials made from selected coals or by certain processes operating at relatively lowtemperatures, for instance, low temperature carbonization processes. In these processes certain intermediate materials produced by fractional distillation of the coal tar material contain substan tial quantities of constituents suitable for use as These constituents are, however, always contaminated with tarry, oxygenated, nitrogenous and other constituents which render them highly unsuitable for use as lubricants. By treating such a material with my liquefied normally gaseous hydrocarbon solvents it is possible to precipitate the contaminating constituents at temperatures somewhat below atmospheric, thereby making it possible to obtain a substantially hydrocarbon material which, with little or no chemical treatment, is suitable for use as a lubricant.

A still further type of process to which my invention can be applied is the treatment of residues from coal tar materials, for instance, road oils and soft pitches, in order to recover valuable by-products therefrom and produce a material more suitable for use on roads, etc. It is known that these materials, when used on roads or as water-proofing agents, should contain a high proportion of alphaltenes and other highly insoluble bodies. By treating such a road oil or soft pitch fraction with my solvents, it is possible to remove a soluble fraction which is valuable as a by-product and at the same time to yield a treated road oil or soft pitch having a greater proportion of-asphaltenes and similar insoluble bodies which render it superior for use as a road treatingmaterial' and/or water-proofing agent.

Although I have described my invention in terms ofzcertain specific embodiments thereof it will readily be understood that numerous other applications are possible within the scope of the principles laid down and I do not wish to be limited-except by the appended claims in which I have set: forth the novel features which I desire to cover.v

I claim: j i

1. The process'ofseparating a coal tar material into a-qfraction of relatively hydrocarbon charaeteristics-andza fraction of relatively nonhydrocarbon -characteristics, which comprises treating said-coal tar. material with a liquefiednormally gaseous hydrocarbon solvent.

2. The process of separating a coal tar material into. a fraction of relatively hydrocarbon characteristics and a fraction of relatively nonhydrocarbon characteristics, which comprises partially..:dissolving said coal tar materials in a liquefied normallygaseous hydrocarbon solvent, separating dissolved and undissolved material, and removing-solvent from said'dissolved and undissolved materials by distillation therefrom.

3. The process of separating a coal tar material into a fraction ofrelatively hydrocarbon characteristics and a. fraction of relatively nonhydrocarbon characteristics, which ,comprises contacting said coal tar material with a liquefied normally gaseous solvent lowering the temperature' of the system by evaporating a portion of said solvent to a point at which immiscible phases are formed, separating said immiscible phases, and removing solvent'from each of said phases by distillation.

4. The method of separating a coal tar material into a. fraction of relatively hydrocarbon characteristics and a fraction of relatively nonhydrocarbon characteristics, which comprises treating said'coa-l tar material with a liquefied normally gaseous hydrocarbon solvent to sub stantially dissolve said first-mentioned fraction without substantially dissolving. said secondmentioned fraction, separating said first-mentioned fraction from said second-mentioned fraction, andremoving the solvent in vapor form from each of said fractions.

5. The method of separating a coal tar material into a fraction of relatively hydrocarbon characteristics and a fraction of relatively nonhydrocarbon characteristics, which comprises treating said coal tar material with a liquefied normally gaseous hydrocarbon solvent at a low temperature to substantially dissolve said firstmentioned fraction without substantially dissolving said second-mentioned fraction, separating said first-mentioned fraction from said secondmentioned fraction, and removing the solvent in vapor form from each of said fractions.

6. The method of purifying crude coal tar materials, containing both phenolic and nonphenolic materials, which comprises treating said material with a liquefied normally gaseous hydrocarbon solvent at reduced temperatures to dissolve non-phenolic materials, removing the dissolved non-phenolic materials, and separately recovering the purified phenolic coal tar material and the non-phenolic materials by removal of solventtherefr-om.

'7. The-method of separating a coal tar materialinto a plurality of fractions which comprises mixing said material with a liquefied normally other of characteristics of hydrocarbon derivatives containing substances of the class consisting of oxygen, sulfur and nitrogen compounds; removing one liquid phase from the other, and

removing the liquefied normally gaseous hydrocarbon from each phase.

8. The method of separating crude coal tar material into a fraction of relatively hydrocarbon characteristics and a fraction of relatively nonhydrocarbon characteristics, which comprises treating said coal tar material with a liquefied normally gaseous solvent consisting substantially of at least one hydrocarbon selected from the.

group consisting of ethane, propane, butane, isobutane, propylene and butlyene, evaporating a substantial portion but substantially less than all of said solvent to lower the temperature of the material undergoing treatment and the residue of said solvent to produce two liquid phases, one of said phases containing said first-mentioned fraction and the greater part of said residue of said solvent, and the'other of said phases containing said second-mentioned fraction and a lesser amount of said solvent, separating said phases from each other, and removing solvent in vapor form from each of said phases.

9. The method of separating a crude coal tar material into a' fraction of relatively hydrocarbon from the other, and distilling each of said layers separately to recover each of said fractions substantially uncontaminated with solvent.

10. The methodof separating a crude coal tar light oil into a fraction of relatively hydrocarbon characteristics and a fraction of relatively nonhydrocarbon characteristics, which comprises treating said crude coal tar light oil with a liquefied normally gaseous hydrocarbon solvent at a low temperature to substantially dissolve said first-mentioned fraction without substantially dissolving said-second-mentioned fraction, separating said first-mentioned fraction from said second-mentioned fraction, and removing said solvent in vapor form from each of said fractions.

11. The method of purifying a crude coal tar light oil containing hydrocarbons, phenols and pyridine bases which comprises treating said crude coal tar light oil with an excess of liquid propane, evaporating a portion but substantially less than all of said liquid propane to lower the temperature of said crude coil tar light oil and the unevaporated residue of saidpropane to a temperature substantially within the range from about -10 F. to about -60 F. at which substantial amounts of each of two liquid phases are formed, one of said liquid phases predominantly containing the hydrocarbon constituents of said crude coal tar light oil and the other of said liquid phases predominantly containing the phenolic and pyridine base constituents of saidcrude coal tar light oil, separating said two liquid phases from each other and removing propane from each of said liquid phases by distillation.

12. The process of separating a coal tar ma.- terial into a fraction of relatively hydrocarbon characteristics and a fraction of relatively nonhydrocarbon characteristics, which comprises treating said coal tar material with liquefied propane.

13. The process of separating a coal tar material into a fraction of relatively hydrocarbon characteristics and a fraction of relatively nonhydrocarbon characteristics, which comprises contacting said coal tar material with liquefied propane, lowering the temperature by evaporating a portion of said propane to a point at which immiscible phases are formed, separating said immiscible phases, and removing said propane from each of said phases by distillation.

14. The method of purifying a coal tar material containing hydrocarbons boiling within the lubricating oil range contaminated with impurities of relatively non-hydrocarbon characteristics, which comprises treating said coal tar ma- .terial with a liquefied normally gaseous hydrocarbon solvent at a temperature adapted to dissolve said hydrocarbons in preference to said non-hydrocarbon impurities, separating the solution from the undissolved material and removing said solvent from said solution.

15. The method of purifying a coal tar material containing hydrocarbons boiling within the lubricating oil range contaminated with impurities of relatively non-hydrocarbon characteristics, which comprises treating said coal tar material with liquefied propane at a temperature adapted to dissolve said hydrocarbons in preference to said impurities, separating the solution from the undissolved material and removing said 1 propane from said solution.

16. The method of purifying a crude phenolic tar material selected from the group exemplified by crude phenol, crude tar acids and crude cresylic acid, contaminated with hydrocarbon 1 soluble impurities, which comprises treating said material with a liquefied normally gaseous hydro-- carbon solvent at a temperature adapted to dissolve at least a substantial amount of said impurities but not to dissolve the phenolic constit-' 1 uents and removing the dissolved impurities from the undissolved phenolic constituents.

17. The method of purifying crude coal tar pyridine contaminated with hydrocarbon impurir ties which comprises treating said crude coal tai pyridine with a liquefied normally gaseous hydrocarbon solvent at a. temperature adapted to dissolve said hydrocarbon impurities but not to dissolve said pyridine 'and separating the dissolved impurities fromthe undissolved pyridine.

18. The method of purifying light coal tar hydrocarbons contaminated with minor quantities of non-hydrocarbon impurities which comprises treating said material with a liquefied normally gaseous hydrocarbon solvent at atemper- 1 ature adapted to dissolve said hydrocarbons but not to dissolve said impurities, separating the undissolved impurities from the solution containing the dissolved hydrocarbons and recovering said hydrocarbons by distilling off the solvent from said solution.

GEORGE L. PARKHURST. 

